Process and apparatus for indirect heat transfer between two liquid materials



May 31, 1938. L. A INSON AL 2,119,091

PROCESS APPAR S FOR IND ECT HEAT TRANSFER WEEN TWO LIQUI ATERIALS d Nov.29. 193

- [ax/44A 2 y Men/uh FOT MED/UM EXCHANGE!- Patented May 31, 1938 UNITEDSTATE a'uaosi PROCESS AND APPARATUS ron 1 HEAT TRANSFER BETWEEN 'rwomourn TERIALS ration of Delaware Application November 29, 1935, SerialNo. 52,204

3 Claims.

This invention relates to a method and means for transferring heat fromone fluid to another,

and has for its particular object the provision of a system in whichheat can be transferred from one medium to another when both mediumshave physical properties such that under the operating conditions theytend to deposit solid matter on the heat transfer surfaces whereby it isnecessary that both mediums be flowed thru tubes which can be easilycleaned. In the appended claims both of these types of materials will bereferred to as materials which tend to deposit solid matter since suchaction usually accompanies decomposition.

A typical example of a heat exchange system to which the presentinvention is applicable is one in which heat is transferred fromcracking coil tar, which is at a hightemperature, to a reduced crudewhich is at a lower temperature. Both of these materials contain aconsiderable quantity of dirty materials and tend to deposit sedimentmore or less readily, which tendency is apparently enhanced by thepresence of the dirt which may contain minerals which accelerate coking.Attempts to transfer heat from one of these mediums to another in aconventional tube and shell heat exchanger have led to grave operatingdifficulties due to plugging up of the shell side of the tube bundlewhich have either discouraged attempts to'transfer the heat from the hotmedium to the cool'medium or have necessitated the employment of specialequipment which ordinarily involved considerable expense.

According to the present invention both mediums of the characterdescribed above are passed through straight, easily cleanable tubes, andheat is transferred from the one to the other through the agency of anauxiliary medium. One of the most important advantages arising from thepresent invention is that it can be carried out by: the employment ofconventional tube and shell heat exchangers connected in such a manneras topermit the flow of the auxiliary medium over the heat transfersurfaces. Another important advantage of this system is that by simplemanipulation of the paths of flow either or both mediums can be passedthrough the heat transizable at the temperature of the heating medium.

When such an auxiliary medium is employed it is used in a quantitysuflicicnt to cover the heating tubes but insuflicient to contact, inthe liquid state, the tubes which bear the medium to be heated. Thecustomary arrangement with such an auxiliary medium consists of twohorizontal tube and shell heat exchangers in superimposed relation, theauxiliary'medium. covering the tubes in the lower shell only, theheating medium being passed through the tubes in the lower unit and themedium to be heated being passed through the tubes in the upper unit-The system; in which heat is transferred by vaporization andcondensation of the auxiliary medium, has several advantages over asystem in which the heat transfer zone is completely filled with liquid.Chief among these advantages is the fact that a much better rate of heattransfer is possible when the auxiliary medium con-. tacts the tubes tobe heated in the vapor phase and condensesthereon than is obtainablewhen the heating medium contacts the'tubes to be heated in the'liquidphase thus reducing the area of heat transfer surface required. In thelatter case, where circulation of the heating medium is efiected purelyby temperature differential, the circulation isusually too sluggish toeffectuate any rapid transfer of heat. To increase the rate and thusreduce the surface required it is necessary to resort to the employmentof circulating pumps to impart higher velocities to the transfer medium.This adds considerably to the cost and operation of the unit.Furthermore,

when the auxiliary heating medium is maintained in the liquid phase itonly transfers sensible heat to the material to be heated, whereas whenit is vaporized it transmits to the material to be heated both sensibleheat and latent heat of vaporization.

Various materials may be employed as the auxiliary medium, the onlyrequirements being that it be chemically heat-stable and vaporizablewithin the temperature range under which it is desired to operate, thatit be in, the liquid state at the lowest operating temperature, and thatit have a suiiiciently high boiling point to permit .the operation ofthe unit at a practicable pressure. In a system in which the heatingmedium enters at a temperature of about GOO-800 F., diphenyl has provenvery satisfactory as an auxiliary medium. The medium selected for anygiven unit, of course, must boil at a temperature below that at whichthe heating medium enters the unit.

When the present invention is practiced with an auxiliary medium whichis maintained in the liquid state throughoutthe heat exchange operation,there is no limitation upon the relative positions of the heat inputchamber and the heat absorption chamber except when the circulation ofthe auxiliary medium is natural and dependent upon gravity, in whichcase it is oviously necessary that the heat absorption chamber be at ahigher level than the heat input chamber.

The preferred embodiment of the present invention is illustrated invertical longitudinal section in the accompanying drawing in which I and2 are conventional tube and shell heat exchangers joined together byenlarged conduits 3 which are Jointed together at 4. In each of units land 2, horizontal parallel tubes 5 are mounted with their ends securedin tube plates 6 and 1. Covering the ends of the tubes in plate 6 is amanifold 8 having on one side an inlet 9 and on the other side an outletl0, and having a partition II mounted between the inlet and outletpoints to divide its interior into two compartments, each of which hasthe same number of tube openings. Mounted over each plate 1 and coveringthe ends of the tubes secured therein is a manifold l2 providingintercommunication between the ends of the tubes. As is apparent, byemploying additional partitions in heads 8 and 12 thus making suitableconnections between the ends of the tubes mounted in plates 6 and I, themedium passing through the tubes may be caused to travel the length ofthe shell several times before it leaves the unit, thus controlling theveloc- I ity of flow in the tubes.

In the arrangement shown on the drawing, the auxiliary medium completelyfills the lower shell. In order to avoid entrainment of auxiliary liquidwith the vapors evolved therefrom, a floating perforated plate l3 can bearranged in the passage formed by conduits 3. The heating medium passesthrough the tubes of the lower unit and the medium to be heated passesthrough the tubes of the upper unit. For example a cracking coil tarentering the lower unit at a temperature of 780 F. and at a rate of72,000#/hr., di-phenyl being the auxiliary medium, will leave the lowerunit at a temperature of 640 F. and will heat a reduced crude enteringthe upper unit at a temperature of 470 F. and at a rate of 254,000#/hr.to a temperature of 505 F.

While the present invention has been described with particular referenceto the exchange of heat between dirty, readily cokable oils, it isapparent that it is of general appliaction. It is a fact, however, thatthe advantages attending the present invention become most significantwhen both the heating'medium and the medium to be heated are of a natureto either deposit sediment, or dement thereof given, what is claimed asnew and useful and desired to be secured by Letters Patent is:

1. A process for indirect heat transfer between two liquid materialseach of which tends to form carbonaceous deposits when heated comprisingpassing the hot liquid material through a series of narrow elongatedpassageways in heat exchange with a body of heat stable liquid in ashell, vaporizing said last mentioned liquid and conducting the vaporssubstantially freed of entrained liquid, into a second shell, passingthe relatively cool liquid material through a series of narrow elongatedpassageways in said shell in heat exchange with said vapors, wherebythey are condensed on said passageways, and returning the condensate tosaid liquid body.

2. A process according to claim 1 in which the liquids tending to formcarbonaceous deposits when heated between which an indirect transfer ofheat is accomplished are a hot cracking coil tar and a relatively coolreduced crude oil.

3. Apparatus for the indirect transfer of heat between two liquidmaterials tending to form carbonaceous deposits when heated by means ofan auxiliary liquid heat exchange medium, comprising, in combination, apair of heat exchanger shells disposed one above the other, an upwardlyextending conduit of enlarged cross section on the lower shell and adownwardly extending conduit on the upper shell, which conduits arejoined to form a passageway between them, a plurality of interconnectedelongated passageways for a relatively cool liquid material disposedwithin said upper shell and a plurality of interconnected elongatedpassageways fora hot liquid material disposed within said lower shell,the passageways within each shell consisting of a plurality of manifoldconnected tubes in which the outer manifold of the bundle forms aclosure for the shell within which it is contained, and provides aseries of inlet and a series of outlet tubes in each bundle, and a bodyof a heat stable liquid heat exchange medium vaporizable at thetemperature of the hot liquid material in said tube bundle contained inthe lower shell and entirely covering the tube bundle therein.

VERNON L. ATKINSON. CLARENCE W. FOSTER.

